Wideband microwave power divider

ABSTRACT

A microwave structure comprising a parallel transmission line that is bisected by a conducting septum to form two independent microstrip circuits that are in anti-phase; i.e., the conducting septum becomes a common ground plane for a pair of equal amplitude microstrip circuits that are in anti-phase relative to the common ground at points equidistant from the point of bisection of the parallel transmission line. In one embodiment, the proprosed microwave structure is utilized as a power divider with input power being supplied to a conventional microstrip circuit formed of a pair of spaced parallel conductor strip members which also form the parallel transmission line and the anti-phase microstrip circuits, and whose widths are varied to form a reflectionless transition from the input microstrip circuit to the parallel transmission line and subsequently to the pair of output microstrip circuits, each of which receives half of the input power supplied to the device.

United States Patent 1 Laughlin 1 Feb. 6, 1973 [54] WIDEBAND MICROWAVEPOWER DIVIDER [75] lnventor: Gordon J. Laughlin, Columbia, Md.

[73] Assignee: The United States of America as represented by theSecretary 01" the Army [22] Filed: Feb. 10,1972

[21] Appl. No.: 225,041

[52] US. Cl ..333/9, 333/11, 333/84 R,

333/84 M, 333/21 R [51] Int. Cl. ..H0lp 1/16, HOlp 3/O8,H01p 5/12 [58]Field of Search.....333/l0, 9, ll, 84, 84 M, 21 R FOREIGN PATENTS ORAPPLICATIONS 2/1960 Great Britain ..333/l0 OUTPUT PORT PrimaryExaminer-Herman Karl Saalbach Assistant Examiner-Marvin NussbaumAtt0mey-R. S. Sciascia et a1.

[57] ABSTRACT A microwave structure comprising a parallel transmissionline that is bisected by a conducting septum to form two independentmicrostrip circuits that are in anti-phase; i.e., the conducting septumbecomes a common ground plane for a pair of equal amplitude microstripcircuits that are in anti-phase relative to the common ground at pointsequidistant from the point of bisection of the parallel transmissionline. In one embodiment, the proprosed microwave structure is utilizedas a power divider with input power being supplied to a conventionalmicrostrip circuit formed of a pair of spaced parallel conductor stripmembers which also form the parallel transmission line and the antiphase microstrip circuits, and whose widths are varied to form areflectionless transition from the input microstrip circuit to theparallel transmission line and subsequently to the pair of outputmicrostrip circuits, each of which receives half of the input powersupplied to the device.

8 Claims, 2 Drawing Figures OUTPUT PORT PAIENTEDFEB 6 ma OUTPUT FIG. 2

WIDEBAND MICROWAVE POWER DIVIDER BACKGROUND OF THE INVENTION In recentyears, the relatively bulky and cumbersome hollow waveguide and circularcoaxial transmission line have been replaced by so-called planartransmission line structures, one class of which is the so-calledmicrostrip circuit wherein electromagnetic waves propagate along anarrow flat strip conductor element dielectrically separated from awider conductive element or ground plane. In certain applications ofthese so-called microstrip circuits or transmission lines; e.g., for usein microwave mixers or antenna difference channels, it is oftendesirable to employ a power divider structure wherein the input power isdivided equally between two output ports in equal amplitude but withvoltages that are 180 out-of-phase. In the past, in order to accomplishthis with the so-called microstrip transmission line, it was necessaryto utilize half wavelength line lengths to achieve the 180 out-of-phaseoutputs. Unfortunately, such a device is frequency dependent in that theanti-phase relationship is attained only at a very select frequency;i.e., the prior art microstrip power divider was very narrow banded.

DESCRIPTION OF THE INVENTION In accordance with the present invention,it is proposed to provide a microwave structure suitable for use as apower divider which is independent of half or quarter wavelengths linesand therefore inherently wideband in operation. Moreover, the proposeddevice provides naturally or inherently for reflectionless transmissionover the entire operating bandwidth where the output characteristicimpedance for each output is equal to one-half the input characteristicimpedance of the device, and the device can also be designed so that itis impedance matched to a common impedance value (e.g. 50 ohms) at allports. The proposed device is also amenable to miniaturization formicrowave integrated circuit applications.

, Basically, the proposed microwave structure of the present inventioncomprises a transmission line of parallel and equal width strips that isbisected by a thin septum of electrically conductive material to formtwo independent microstrip circuits that are in anti-phase.More-particularly, it is well-known to those skilled in the art that theelectric and'magnetic fields of a parallel transmission line conductorpair of equal width mounted one above the other on an interveningdielectric substrate are mirror images about a plane midway between thelines.

In accordance with the present invention, it is proposed that aconducting septum be inserted along a plane midway between theparalleltransmission line conductors without disturbing the magnetic or electricfield configurations. As a result, the power contained above the imageplane (conducting septum) is equal to the power below the image plane,and relativeto the image plane or conducting septum the electric fieldsabove and below this plane are in anti-phase. Because the fieldconfigurations are not altered by the presence of the conducting septum,the parallel transmission line appears continuous. On the other hand,once the conducting septum is inserted, as proposed in accordance withthe present invention, the upper and lower conductors are no longerrequired to lie one directly above the other as is the case with theparallel transmission line; i.e., the conductors can be taken inseparate directions in their respective plane and the fieldconfigurations above the image plane (septum) will be preserved relativeto the upper conductor and the field configurations below the imageplane (septum) will be preserved with regard to the lower conductor.

As will be described in more detail hereinafter, the fieldconfigurations associated with the upper and lower conductor elementsare those of a microstrip line, and relative to the conducting septumthe voltages of the upper and lower conductors are in anti-phase atpoints equidistant from'the point: of insertion of conducting septum.Moreover, the power propagated by upper conductor above the conductingseptum is equal to the power propagated by the lower conductor belowconducting septum. The conducting septum, therefore, becomes commonground plane for a pair of equal am plitude microstrip circuits that arein anti-phase relative to the commonground plane.

In view of the foregoing, one object of the present invention is toprovide a microwave structure for converting a parallel transmissionline into a pair of antiphase microstrip circuits.

Another object of the present invention is to provide a microwavestructure capable of being utilized to perform broadband, equal powerdivision of input microwave power.

Another object of the present invention is to provide a microwavestructure having application as a reflectionless power divider whoseoutputs are in anti-phase relative to a common ground conductor andwhich is inherently broadband, compact, of very simple construction, andamenable to microminiaturization.

Other objects, purposes and characteristic features of the presentinvention will in part be pointed out as the description of the presentinvention progresses and in part be obvious from the accompanyingdrawings, wherein:

FIG. I is an isometric view of a power divider structure constitutingone embodiment of the present inven- .tion; and

FIG. 2 is an enlarged partial cross-sectional view of the centralparallel transmission line portion of the power divider structure ofFIG. 1.

In the powerdivider embodiment shown in FIG. 1 of the drawings, asuitabledielectric member formed of alumina (e, E 9) or like materialand designated at 10 supports a pair of electrical conductor members 1 land 12 formed of flat copper strips, for example. These conductor strips11 and 12 have substantially L-shaped configurations at the respectiveright-hand ends thereof, as viewed in FIG. 1. Also carried in thedielectric l0, midway between the spaced-apart conductor strip members11 and 12, is a suitable thin sheet or septum 13 formed of suitableelectrically conductive material such as, for example, 0.003 inchaluminum foil.

The left-hand end of the upper conductor strip 11 is 0.050 inch aluminaas the dielectric block for a 50 ohm transmission line, the width of thelefthand end portion of the upper conductor strip 1 l was 0.050 inch;whereas, the enlarged end portion of the lower conductor strip 12 (whichideally would be infinitely wide) was found to function successfullywith a 2 inch width.

On the other hand, the midportions of the upper and center portions ofthe conductor strips 11 and 12. It

should be noted here that the variation in width between the left-handend and center portion of the upper conductor strip 1 1 is for thepurpose of attaining a constant characteristic impedance transition'when proceeding from the left-hand or microstrip input end of thestructure into the central or parallel transmission line portion. On theother hand, by making the righthand or output ends of conductors 11 and12 of a width equal to the central portions, the characteristicimpedance of each of the output microstrip circuits is one-half that ofthe parallel transmission line, in order to also achieve reflectionlesstransmission therebetween.

Referring now to the cross-sectional view of FIG. 2 taken, as mentionedpreviously, at the parallel transmission line portion of the illustrateddevice, the electric and magnetic fields of such a parallel transmissionline with an intervening dielectric substrate are mirror images about aplane midway between the line conductors 11 and 12, as shown. In FIG. 2the electric field lines are shown in solid line form and the magneticfield lines are shown as dashed lines. Relative to the designated imageplane which is midway between conductors 11 and 12, the electric fieldsabove and below the image plane are in anti-phase and the microwavepower contained above the illustrated image plane is equal to the powerbelow the image plane. Accordingly, the conducting septum 13 can beinserted along this image plane, as shown in FIG. 1, without disturbingthe field configurations and therefore the parallel line appearscontinuous. Once the septum 13 is inserted, however, the upper and lowerconductor strips 11 and 12 are no longer required to lie one directlyabovethe other, as in the parallel transmission line portion. Thus, theextending right-hand ends of the conductors 11 and 12 can now be takenin separate directions in their respective planes; e.g., takenperpendicular to the direction of the parallel transmission lineportions as shown in FIG. 1, and the field configurations above theimage plane (septum 13) will still be preserved with regard to the upperconductor strip 11 and the field configurations below the image plane(septum 13) will be preserved with regard to the lower conductor strip12. As a result, the voltages of the upper and lower conductors 11 and12 relative to the conducting septum 13 are in anti-phase at pointsequidistant from the plane of insertion of the conducting septum 13. Theseptum 13 thus becomes a common ground plane for a pair of equalamplitude microstrip circuits that are in anti-phase relative to thecommon ground at points equidistant from the plane of bisection of theparallel transmission line pair.

As shown in the power divider embodiment of FIG. 1 input microwave powerto the divider structure is applied to a microstrip circuit formed bythe left-hand ends of the upper and lower conductor strip members 11 and12. In particular, the enlarged left-hand end of the lower conductorstrip 12 functions as the ground plane for the input microstrip circuitand the width of the upper conductor strip 11 determines thecharacteristic impedance of this input microstrip circuit. On the otherhand and as mentioned hereinabove, the widths of the parallel lineconductors; e.g., the midportions of the conductor strips 11 and 12, areequal to one another and to the width of the output microstripconductors but different from that of the input microstrip in order toachieve reflectionless transmission throughout the structure. Moreover,the fact that the field configurations are not disturbed by the presenceof the conducting septum 13 also facilitates the reflectionlesstransmission of power section to the parallel line section to the twooutput microstrip circuits. The resulting three dimensional microstripcircuit is thus a reflectionless power divider whose outputs are inantiphase relative to the common ground plane 13; it'is inherentlybroadband, compact, very simply constructed and amenable tomicrominiaturization; and, requires only that the two output microstriparm segments be of equal length. The characteristic impedance of each ofthese two output microstrip circuits is equal to one-half that of thecentral of parallel transmission ,line portion of the device. It shouldbe understood at this time that the illustrated microstrip input to thetransmission line pair of the proposed structure is only one manner ofapplying input microwave energy to the transmission line pair. By way ofexample, this input microstrip circuit might be replaced by acoaxial-to-parallel transmission line pair transition structure, etc.

Suitable coaxial-to-microstrip transitions on either side of thesubstrate 10 can provide a pair of coaxial outputs from the proposeddevice which are in antiphase relative to their outer conductors, orimaginative transitions could be used for a pair of anti-phase planarmicrostrip or strip line outputs. If the input port and the two outputports of the proposed power divider are to have the same impedance,tapers or quarterwavelength impedance matching transformers can, ifdesired, be incorporated into the divider. Tapers would be the betterchoice here since they tend to have ultra broad-band characteristicsabove a cutoff frequency determined by the length of the taper.Moreover, the taper could be designed into each microstrip arm or thewhole divider could be formed as one continuous taper.

Various other modifications, adaptations and alterations are of coursepossible in light of the above teachings. It should therefore beunderstood at this time that within the scope of the appended claims theinvention may be practiced otherwise than as specifically describedhereinabove.

What is claimed is:

l. A microwave structure comprising,

a parallel line transmission line formed of a pair of electricallyconductive line members separated by a dielectric material and disposedin spaced parallel planes, and

a septum member formed of electrically conductive material disposed in aplane bisecting the distance between the spaced parallel planes of saidpair of transmission line members and cooperating with equal lengths ofeach of said transmission members for converting said parallel linetransmission line to a pair of equal amplitude, anti-phase microstripcircuits.

2. The microwave structure specified in claim 1 wherein said parallelline members are in the form of a pair substantially thin flat stripmembers having portions disposed one above the other and extending inthe same direction to form the line members of a parallel linetransmission line.

3. The microwave structure specified in claim 2 wherein said pair ofstrip members include respective second portions which are of equallength and which extend in different directions relative to one anotherand relative to said same direction and cooperate with said septummember to form a pair of microstrip circuits with spaced apart outputports.

4. The microwave structure specified in claim 3 wherein said secondportion of each of said strip members extend in opposite directionsperpendicular to said same direction.

5. The microwave structure specified in claim 1 further including a,pair of spaced elements separated from one another by said dielectricmaterial and forming a microstrip input operably connected to saidparallel line transmission line elements.

6. The microwave structure specified in claim 3 wherein saidelectrically conductive strip members have third portions configured toform an input microstrip circuit operably connected adjacent thoseportions of said strip members forming said parallel line transmissionline.

7. The microwave structure specified in claim 6 wherein said thirdportions include a portion of each of said strip members formingrespectively a conductor and ground plane element for said microstripinput circuit.

8. The microwave structure specified in claim 7 wherein the respectivewidths of said electrically conductive strip members is varied tomaintain a constant characteristic impedance between the input to saidinput microstrip circuitand the output ports formed by said stripmembers and said conductive septum.

1. A microwave structure comprising, a parallel line transmission lineformed of a pair of electrically conductive line members separated by adielectric material and disposed in spaced parallel planes, and a septummember formed of electrically conductive material disposed in a planebisecting the distance between the spaced parallel planes of said pairof transmission line members and cooperating with equal lengths of eachof said transmission members for converting said parallel linetransmission line to a pair of equal amplitude, anti-phase microstripcircuits.
 1. A microwave structure comprising, a parallel linetransmission line formed of a pair of electrically conductive linemembers separated by a dielectric material and disposed in spacedparallel planes, and a septum member formed of electrically conductivematerial disposed in a plane bisecting the distance between the spacedparallel planes of said pair of transmission line members andcooperating with equal lengths of each of said transmission members forconverting said parallel line transmission line to a pair of equalamplitude, anti-phase microstrip circuits.
 2. The microwave structurespecified in claim 1 wherein said parallel line members are in the formof a pair substantially thin flat strip members having portions disposedone above the other and extending in the same direction to form the linemembers of a parallel line transmission line.
 3. The microwave structurespecified in claim 2 wherein said pair of strip members includerespective second portions which are of equal length and which extend indifferent directions relative to one another and relative to said samedirection and cooperate with said septum member to form a pair ofmicrostrip circuits with spaced apart outpUt ports.
 4. The microwavestructure specified in claim 3 wherein said second portion of each ofsaid strip members extend in opposite directions perpendicular to saidsame direction.
 5. The microwave structure specified in claim 1 furtherincluding a pair of spaced elements separated from one another by saiddielectric material and forming a microstrip input operably connected tosaid parallel line transmission line elements.
 6. The microwavestructure specified in claim 3 wherein said electrically conductivestrip members have third portions configured to form an input microstripcircuit operably connected adjacent those portions of said strip membersforming said parallel line transmission line.
 7. The microwave structurespecified in claim 6 wherein said third portions include a portion ofeach of said strip members forming respectively a conductor and groundplane element for said microstrip input circuit.